Coated fiber cement article with crush resistant latex topcoat

ABSTRACT

A coated fiber cement article in the form of an unattached fiber cement board roofing tile or roofing slate substrate having a first major surface at least a portion of which is covered with a crush resistant final topcoat composition comprising a multistage latex polymer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/472,321 filed May 15, 2012, now allowed, which is a divisional ofU.S. application Ser. No. 11/560,329 filed Nov. 15, 2006, entitled CrushResistant Latex Topcoat Composition for Fiber Cement Substrates, nowU.S. Pat. No. 8,202,578 B2, which in turn claims priority to U.S.Provisional Application Ser. No. 60/737,442 filed Nov. 15, 2005, theentire disclosures of which are incorporated herein by reference.

FIELD

This invention relates to prefinished fiber cement siding.

BACKGROUND

Fiber cement composite siding is a high quality building material thathas many advantages over vinyl, aluminum or wood siding. One majoradvantage is the significantly better durability of fiber cement siding.Fiber cement siding typically includes a substrate made from wood pulpor synthetic fiber mixed with silica, hydraulic cement and water. Themixture is pressed into board form and dried. One or both major surfacesof the siding may be profiled or embossed to look like a grained orroughsawn wood or other building product, or scalloped or cut toresemble shingles. A variety of siding styles or shapes are available,including lap siding, vertical siding, soffit panels, trim boards,shaped edge shingle replicas and stone or stucco replicas, all of whichmay be collectively referred to as “boards”. Fiber cement siding boardsare also available in a variety of sizes and thicknesses. For example,vertical siding sheets typically have a width of about 1.2 m (4 ft),lengths of about 2.5 to 3 m (8 to 10 ft) and thicknesses of about 4 to15 mm (0.16 to 0.59 in). Fiber cement siding boards may be prefinished(e.g., primed or painted) at the factory where they are made, stored instacks (e.g., in a warehouse at the factory or at a distributor), anddelivered to a job site ready for attachment to a building. Theresulting prefinished board has a primed or painted appearanceimmediately upon attachment.

Unfortunately, however, fiber cement siding is a much heavier substratecompared to vinyl, aluminum or wood siding products. While builders andhomeowners desire the beauty and convenience of fiber cement siding, thedecorative surface of a prefinished board can be visually marred ordamaged during storage. If the damaged preapplied finish is merely aprimer, then the consequences are not so severe. After attachment to abuilding, the preprimed board can be coated with a final topcoat, a stepthat would have been carried out in any event. However, if the damagedpreapplied finish is a final topcoat, then at least the damaged portionand often the entire board will have to be refinished. This defeats thepurpose of manufacturing boards with a preapplied final topcoat.

One damage mechanism is caused when the heavy boards are stacked atopone other, and the accumulated board weight damages the finish. Forexample, the primed or painted peaks of an embossed siding surface canbe crushed, and the flattened peaks can appear as glossy spots.Manufacturers attempt to reduce such damage by placing pairs ofprefinished boards in face-to-face relationship with a protectiveplastic or paper liner between the prefinished face surfaces. Theresulting board pairs may be stacked on a pallet, e.g., at a palletheight of about 30 to about 60 cm (about 1 to about 2 ft), and if theliner has sufficient thickness it may adequately protect the surface ofboards within the pallet. However, in order to maximize warehousecapacity a manufacturer or distributor may also stack multiple palletsof siding boards directly atop one another, using spacing planks toprovide forklift access between each pallet. The bottom boards in such amultiple pallet stack carry the weight of all the boards that arestacked above them. In tall warehouses the weight against the bottomboards may exceed 6, 8 or even 10 kg/cm² (85, 113 or even 142 psi), anddamage to the finish on such bottom boards can be severe despite thepresence of the protective liner. Also, portions of the boards beneaththe spacing planks may be subjected to a more concentrated load (viz.,pressure) than portions not directly beneath the spacing planks, andlocalized finish damage may telegraph through one or more boardsdirectly beneath the spacing planks.

From the foregoing, it will be appreciated that what is needed in theart is a prefinished fiber cement siding product that maintains itsfactory appearance during storage in multiple pallet stacks, e.g., intall warehouses. Such siding products and methods for preparing the sameare disclosed and claimed herein.

SUMMARY

Surprisingly, we have discovered that a final topcoat compositioncomprising a multistage latex polymer can withstand the forces that maybe imparted during the storage of fiber cement siding products. Forexample, final topcoat compositions containing a multistage latexpolymer having a sufficiently low “soft stage” Tg and a sufficientlyhigh “hard stage” Tg appear to provide a crush-resistant, readilycoalesceable final topcoat. The soft stage Tg preferably is such thatthat the composition will coalesce at a Minimum Film Forming Temperature(MFFT) between about 0 and about 55° C. without requiring more than 10%VOCs for acceptable film formation. The hard stage Tg preferably is suchthat the coated boards may be stacked on the forklift pallets normallyused in fiber cement board manufacturing facilities without exhibitingevidence of crush damage, and more preferably is such that multiplepallets may be stacked atop one another without causing such damage.

Accordingly, in one embodiment the present invention provides a coatedfiber cement article comprising an unattached fiber cement boardsubstrate having a first major surface at least a portion of which iscovered with a crush resistant final topcoat composition comprising amultistage latex polymer.

In another embodiment the present invention provides a method for makinga coated fiber cement article, which method comprises providing anunattached fiber cement board substrate having a first major surface;providing a topcoat coating composition comprising a multistage latexpolymer; applying the topcoat coating composition to at least a portionof the first major surface; drying or otherwise hardening the coatingcomposition to form a crush resistant final topcoat; and stacking two ormore of the thus-coated boards on a pallet or other horizontalsupporting surface.

In further preferred embodiments, a pair of the coated boards is placedin face-to-face relationship with a protective plastic or paper linerbetween the topcoated surfaces, or a plurality of such pairs are stackedon a fork lift platform to provide a loaded pallet, or multiple palletsloaded with the coated boards are stacked atop one another.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic cross-sectional view of a coated fiber cementarticle;

FIG. 2 is a schematic cross-sectional view of a face-to-face pair ofcoated fiber cement articles with a protective liner therebetween;

FIG. 3 is a perspective view of a pallet of coated fiber cementarticles;

FIG. 4 is a perspective view of a multiple pallet stack of coated fibercement articles;

FIG. 5 through FIG. 11 are differential scanning calorimetry (DSC)curves showing Tg values for various latex polymers.

Like reference symbols in the various figures of the drawing indicatelike elements. The elements in the drawing are not to scale.

DETAILED DESCRIPTION

The recitation of a numerical range using endpoints includes all numberssubsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, 5, etc.).

The terms “a,” “an,” “the,” “at least one,” and “one or more” are usedinterchangeably. Thus, for example, a coating composition that contains“an” additive means that the coating composition includes “one or more”additives.

The term “board” refers to a generally planar component suitable forattachment to a building exterior surface, including lap siding,vertical siding, soffit panels, trim boards, shingle replicas, stonereplicas and stucco replicas.

The phrase “chalk resistant” when used with respect to a coatingcomposition means that if the coating composition is applied to anddried or otherwise hardened on a fiber cement board substrate, thecoating composition will have a chalk rating not less than 5 (viz., arating of 5 to 10), more preferably not less than 6 (viz., a rating of 6to 10) and most preferably not less than 8 (viz., a rating of 8 to 10)when evaluated according to ASTM D 4214 Test Method A using a 5 yearvertical exterior exposure in Florida.

The phrase “color change resistant” when used with respect to a coatingcomposition means that if the coating composition is applied to anddried or otherwise hardened on a fiber cement board substrate, thecoating composition will change less than 15 Macadam units, morepreferably will change less than 10 Macadam units, and most preferablywill change less than 8 Macadam units following a 5 year verticalexterior exposure in Florida.

The phrase “crack resistant” when used with respect to a coatingcomposition means that if the coating composition is applied to anddried or otherwise hardened on a fiber cement board substrate, thecoating composition will have a crack rating not less than 5 (viz., arating of 5 to 10), more preferably not less than 6 (viz., a rating of 6to 10) and most preferably not less than 8 (viz., a rating of 8 to 10)when evaluated according to ASTM D 661 using a 5 year vertical exteriorexposure in Florida.

The phrase “crush resistant” when used with respect to a coatingcomposition means that if the coating composition is applied to anddried or otherwise hardened on two face-to-face embossed fiber cementboard substrates, and subjected to a pressure of about 6 kg/cm2, thecoating will exhibit a rating of 3 or better when visually assessedusing the 1 to 5 rating scale described below.

The phrase “final topcoat” refers to a coating composition which whendried or otherwise hardened provides a decorative or protectiveoutermost finish layer on a fiber cement board attached to a buildingexterior. By way of further explanation, such final topcoats includepaints, stains or sealers capable of withstanding extended outdoorexposure (e.g., exposure equivalent to one year of vertical south-facingFlorida sunlight) without visually objectionable deterioration, but donot include primers that would not withstand extended outdoor exposureif left uncoated with a topcoat.

The term “functionalized” when used with respect to a latex polymermeans the polymer contains additional pendant reactive chemical moietiesother than carboxylic acid groups and linear, branched or ringstructures containing (CH_(x)) groups where x is 0, 1, 2, or 3.

The term “gloss” when used with respect to a coating composition meansthe 60° measurement obtained when evaluating a smooth region of a fibercement board major surface according to ASTM D 523.

The term “loaded” when used with respect to a pallet means that thepallet contains a stack of four or more boards.

The phrase “low levels” when used with respect to a multistage latexpolymer containing or made from styrene means that less than 30 wt. %styrene (based upon the total weight of ethylenically unsaturatedmonomers employed) is present in or was used to form the multistagelatex polymer; “very low levels” means that less than 20 wt. % styreneis present in or was used to form the multistage latex polymer, and“substantially free of” means that less than 10 wt. % styrene is presentin or was used to form the multistage latex polymer.

The phrase “low VOC” when used with respect to a liquid coatingcomposition means that the coating composition contains less than about10 wt. % volatile organic compounds, more preferably less than about 7%volatile organic compounds, and most preferably less than about 4%volatile organic compounds based upon the total liquid coatingcomposition weight.

The term “(meth)acrylic acid” includes either or both of acrylic acidand methacrylic acid, and the term “(meth)acrylate” includes either orboth of an acrylate and a methacrylate.

The term “multistage” when used with respect to a latex means the latexpolymer was made using discrete charges of two or more monomers or wasmade using a continuously-varied charge of two or more monomers. Usuallya multistage latex will not exhibit a single Tg inflection point asmeasured using DSC. For example, a DSC curve for a multistage latex madeusing discrete charges of two or more monomers may exhibit two or moreTg inflection points. Also, a DSC curve for a multistage latex madeusing a continuously-varied charge of two or more monomers may exhibitno Tg inflection points. By way of further explanation, a DSC curve fora single stage latex made using a single monomer charge or a non-varyingcharge of two monomers may exhibit only a single Tg inflection point.Occasionally when only one Tg inflection point is observed it may bedifficult to determine whether the latex represents a multistage latex.In such cases a lower Tg inflection point may sometimes be detected oncloser inspection, or the synthetic scheme used to make the latex may beexamined to determine whether or not a multistage latex would beexpected to be produced.

The term “pallet” refers to a portable warehousing platform upon whichboards can be stacked and which can be moved within a warehouse using aforklift.

The phrase “flake resistant” when used with respect to a coatingcomposition means that if the coating composition is applied to anddried or otherwise hardened on a fiber cement board substrate, thecoating composition will maintain a flake rating not less than 5 (viz.,a rating of 5 to 10), more preferably not less than 6 (viz., a rating of6 to 10) and most preferably not less than 8 (viz., a rating of 8 to 10)when evaluated according to ASTM 772 using a 5 year vertical exteriorexposure in Florida.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

The term “pressure” when used with respect to a stack of pallets refersto the estimated or measured maximum pressure on a discernible region(e.g., an embossing peak) for the uppermost board on the lowermostpallet in the stack. This uppermost or top board tends to receive a veryconcentrated load in the regions directly beneath the pallet (e.g.,under a pallet plank). Although boards beneath this top board may beareven greater total weight, such weight tends to be relatively evenlydistributed with lower peak area loads than is the case directly beneatha pallet.

The term “unattached” when used with respect to a board means that theboard has not been fastened (e.g., nailed, screwed or glued) to abuilding.

The phase “weather resistant” when used with respect to a coatingcomposition means that the coating composition is at least one or moreof (and more preferably at least two or more of, yet more preferably atleast three or more of and most preferably all of) chalk resistant,color change resistant, crack resistant or flake resistant when exposedoutdoors.

Referring to FIG. 1, a coated fiber cement board 10 of the presentinvention is shown in schematic cross-sectional view. Board 10 includesa fiber cement substrate 12. Substrate 12 typically is quite heavy andmay for example have a density of about 1 to about 1.6 g/cm³ or more.The first major surface 14 of substrate 12 may be embossed with smallpeaks or ridges 16 and valleys 18, e.g., so as to resemble roughsawnwood. Major surface 14 may have a variety of other surfaceconfigurations, and may resemble a variety of building materials otherthan roughsawn wood. An optional further layer or layers 20 (which mayfor example be a sealer, primer or layers of both sealer and primer) maylie atop surface 14. Layer 20 can provide a firmly-adhered base layerupon which one or more firmly-adhered layers of final topcoat 22 may beformed, and may hide mottling or other irregularities (arising in someinstances when the board is dried at the factory) which may otherwise bevisible on surface 14. If a primer, layer 20 may include a high PigmentVolume Concentration (PVC), e.g., about 45% or more. Layer 20 is howevernot weather-resistant or decorative and is not designed or intended toserve as a final topcoat. Final topcoat 22 provides a crush resistantsurface that is weather-resistant and decorative and which resistsdamage when additional boards are stacked atop article 10. Final topcoat22 desirably withstands the forces that may be imparted to board 10during other warehousing and shipping operations such as long-termstorage and transporting of prefinished stacked boards 10 to a jobsite.Final topcoat 22 thus may provide reduced visual coating damage and,consequently, less need for touch-up repairs or recoating after board 10has been attached to a building.

The differences in height between peaks 16 and valleys 18 in majorsurface 14 typically are much greater than those shown in FIG. 1; thethicknesses of primer layer 20 and final topcoat 22 have been magnifiedin FIG. 1 for emphasis. The typical actual differences in height betweenpeaks 16 and valleys 18 in major surface 14 may for example be about 1to about 5 mm.

FIG. 2 shows a schematic cross-sectional view of a face-to-face pair 24of coated fiber cement boards 10 a, 10 b whose embossed faces 14 a, 14 bmay be covered with optional primer, optional sealer or both primer andsealer (not shown in FIG. 2) and final topcoats 22 a, 22 b. Finaltopcoats 22 a, 22 b face one another but are separated and protectedsomewhat from damage by protective liner 26 located between finaltopcoats 22 a, 22 b. The arrangement shown in FIG. 2 can provide bettercrush resistance when tall stacks of boards 10 are piled atop oneanother.

FIG. 3 shows a perspective view of a loaded pallet 30 including a pallet32 upon which has been loaded a plurality of eight board pairs 24 athrough 24 h. Optional strapping tape 34 helps stabilize loaded pallet32. Cross beams 35 sandwiched between upper horizontal platform 36 andlower horizontal platform 37 also stabilize loaded pallet 32. Personshaving ordinary skill in the art will recognize that other palletconfigurations may be employed. For example, the pallet may include morecross-beams 35 (e.g., three, four, five or more) or may omit lowerhorizontal platform 37. Persons having ordinary skill in the art willrecognize that pallet 32 may be loaded with fiber cement boards havingshapes other than the large siding boards shown in FIG. 3. For example,a pallet may be loaded with rows of side-by-side planks, soffit panels,trim boards, shingles, stone replicas, stucco replicas and otheravailable board configurations. Persons having ordinary skill in the artwill also recognize that the height of a loaded pallet 32 may vary, andfor example may be about 0.2 to about 2 meters.

FIG. 4 shows a perspective view of a two side-by-side stacks 40 each ofwhich contains three loaded pallets 32 placed atop one another. AlthoughFIG. 4 shows three pallets in each stack, the stacks may contain more orfewer pallets and may have a variety of overall heights. The pallet maynot evenly distribute the weight, and the pallet cross beams mayconcentrate the pallet weight on peak regions within the embossedsurface of boards beneath the pallet. Thus in practice all the overlyingboard weight may be exerted onto as little as 5-10% of the total boardsurface area. For example, using currently-available palletizing systemsdesigned for fiber cement siding, coated fiber cement boards may bestacked up to about 6 meters high. For such a 6 meter stack, theresulting pressure (based on about 5-10% contact area) upon theuppermost board in the lowermost pallet of the stack may for example beabout 10 kg/cm², and may be about 8 kg/cm² when the stack is 4 metershigh and about 6 kg/cm² when the stack is 2 meters high.

A variety of fiber cement board substrates may be employed in thepresent invention. Such substrates will usually include a composite ofwood pulp (e.g., containing cellulosic fibers), silica and hydrauliccement (e.g., Portland cement). Representative fiber cement substratesfor use in the present invention include uncoated fiber cementsubstrates, sealed but unprimed fiber cement substrates, preprimed andoptionally sealed fiber cement substrates, and prepainted and optionallyprimed or sealed fiber cement substrates. Whether or not already coatedas obtained, the substrate may optionally be further primed, stained orsealed as desired, then topcoated as described herein. A variety ofsuitable fiber cement substrates are commercially available. Forexample, several preferred fiber cement siding products are availablefrom James Hardie Building Products Inc. of Mission Viejo, Calif.,including those sold as HARDIEHOME™ siding, HARDIPANEL™ vertical siding,HARDIPLANK™ lap siding, HARDIESOFFIT™ panels, HARDITRIM™ planks andHARDISHINGLE™ siding. These products are available with an extendedwarranty, and are said to resist moisture damage, to require only lowmaintenance, to not crack, rot or delaminate, to resist damage fromextended exposure to humidity, rain, snow, salt air and termites, to benon-combustible, and to offer the warmth of wood and the durability offiber cement. Other suitable fiber cement siding substrates includeAQUAPANEL™ cement board products from Knauf USG Systems GmbH & Co. KG ofIserlohn, Germany, CEMPLANK™, CEMPANEL™ and CEMTRIM™ cement boardproducts from Cemplank of Mission Viejo, Calif.; WEATHERBOARDS™ cementboard products from CertainTeed Corporation of Valley Forge, Pa.;MAXITILE™, MAXISHAKE™ AND MAXISLATE™ cement board products from MaxiTileInc. of Carson, Calif.; BRESTONE™, CINDERSTONET™, LEDGESTONE™, NEWPORTBRICK™, SIERRA PREMIUM™ and VINTAGE BRICK™ cement board products fromNichiha U.S.A., Inc. of Norcross, Ga., EVERNICE™ cement board productsfrom Zhangjiagang Evernice Building Materials Co., Ltd. of China and EBOARD™ cement board products from Everest Industries Ltd. of India.

The disclosed coated boards include one or more layers of a finaltopcoat. For example, in one exemplary embodiment the board is coatedwith a sealer layer and one or more final topcoat composition layers. Inanother exemplary embodiment the board is coated with a primer layer andone or more final topcoat composition layers. In yet another exemplaryembodiment, the board is coated with a sealer layer, a primer layer andone or more final topcoat composition layers. Preferably, the variouslayers are selected to provide a coating system that has good adhesionto the substrate and between adjacent layers of the system.

Representative optional sealer layers include acrylic latex materials.The sealer layer may for example provide one or more features such asimproved adhesion, efflorescence blocking, water resistance or blockresistance. Exemplary sealers include unpigmented or low pigment levellatex solutions containing, for example, between about 5 and 20 wt. %solids. An example of a commercially available sealer is OLYMPIC™ FCsealer (available from PPG). Other sealers include those described inU.S. Provisional Application Nos. 60/764,044, 60/764,103, 60/764,131 and60/764,242 (each of which was filed Jan. 31, 2006), 60/802,185 and60/802,186 (both filed May 19, 2006), 60/810,739 (filed Jun. 2, 2006)and 60/819,505 (filed Jul. 7, 2006). The disclosure of each of theseProvisional applications is incorporated herein by reference. Arecommended thickness for the sealer after it is dried or otherwisehardened is about 0.1 to about 0.3 mm.

Representative optional primer layers include acrylic latex or vinylprimers. The primer may include color pigments, if desired. Preferredprimers have a measured 60° gloss value less than 15 gloss units, morepreferably less than 10 gloss units, and most preferably less than 5gloss units, and a PVC of at least 45%. Preferred primers also provideblocking resistance. A recommended thickness for the primer after it isdried or otherwise hardened is about 10 to 50 micrometers and morepreferably about 15 to about 30 micrometers.

A variety of final topcoat compositions may be used in the presentinvention. The topcoat includes a multistage latex polymer, typicallywill include a carrier (e.g., water or one or more organic solvents),may include other ingredients such as color pigments if desired, and insome embodiments could be characterized as a paint. Preferably, thefinal topcoat is formulated so that it can be applied and hardened oncement substrates using factory application equipment that moves theboard past a coating head and suitable drying or curing equipment.Preferred final topcoat compositions have a measured 60° gloss valuegreater than 1 gloss unit, and more preferably between 5 and 30 glossunits.

A variety of multistage latex polymers may be used in the disclosedfinal topcoats. The multistage latex preferably contains at least twopolymers of different glass transition temperatures (viz., different Tgvalues). In one preferred embodiment, the latex may include a firstpolymer stage (the soft stage) having a Tg less than 40° C., e.g.,between about −65 and 40° C. and more preferably between about −15 and15° C., and a second polymer stage (the hard stage) having a Tg greaterthan 40° C., e.g., between about 40 and 230° C. and more preferablybetween about 60 and 105° C.

Multistage latexes are conveniently prepared using emulsionpolymerization and sequential monomer feeding techniques. For example, afirst monomer composition is fed during the early stages of thepolymerization, and then a second different monomer composition is fedduring later stages of the polymerization. In certain embodiments it maybe favorable to start the polymerization with a high Tg monomercomposition and then switch to a low Tg monomer composition, while inother embodiments, it may be favorable to start the polymerization witha low Tg monomer composition and then switch to a high Tg monomercomposition. Numerous hard and soft stages may also be utilized. Forexample, in certain compositions it may be beneficial to polymerize twodifferent low Tg soft stage monomer compositions. In an illustrativeembodiment, the first soft stage may be prepared with a monomercomposition Tg close to room temperature (e.g., 20° C.) and the secondsoft stage may be prepared with monomer composition Tg well below roomtemperature (e.g., less than 5° C.). While not intending to be bound bytheory, it is believed that this second soft stage polymer assists inimproving coalescence of the latex polymer particles.

It may be advantageous to use a gradient Tg latex polymer made usingcontinuously varying monomer feeds. The resulting polymer will typicallyhave a DSC curve that exhibits no Tg inflection points, and could besaid to have an essentially infinite number of Tg stages. For example,one may start with a high Tg monomer feed and then at a certain point inthe polymerization start to feed a low Tg soft stage monomer compositioninto the high Tg hard stage monomer feed. The resulting multistage latexpolymer will have a gradient Tg from high to low. In other embodiments,it may be favorable to feed a high Tg hard stage monomer compositioninto a low Tg soft stage monomer composition. A gradient Tg polymer mayalso be used in conjunction with multiple Tg polymers. As an example,one may employ a high Tg monomer feed (F1) and a low Tg monomer feed(F2), with the F2 feed being directed into the F1 monomer vessel, andthe feed from the F1 vessel being directed into the latex reactorvessel. Polymerization could begin with feed F2 being turned off andfeed F1 being sent into the latex reactor vessel to initiatepolymerization. After polymerization is underway, one could feed F2 intoF1 at a faster F2 feed rate than the overall F1+F2 feed rate into thereactor vessel, and in this example provide reduced Tg “soft stage”polymer particles with a higher Tg core and a gradient Tg shell.

The disclosed multistage latex polymer compositions preferably includeabout 5 to about 95 weight percent soft stage polymer morphology basedon total polymer weight, more preferably about 50 to about 90 weightpercent soft stage polymer morphology based on total polymer weight, andmost preferably about 60 to about 80 weight percent soft stage polymermorphology on total polymer weight. The disclosed multistage latexpolymer compositions preferably include about 5 to 95 weight percenthard stage polymer morphology on total polymer weight, more preferablyabout 10 to about 50 weight percent hard stage polymer morphology ontotal polymer weight, and most preferably about 20 to about 40 weightpercent hard stage polymer morphology on total polymer weight.

The disclosed final topcoat compositions preferably include at leastabout 10 wt. %, more preferably at least about 25 wt. %, and yet morepreferably at least about 35 wt. % multistage latex polymer based on thetotal composition solids. The disclosed final topcoat compositions alsopreferably include less than 100 wt. %, more preferably less than about85 wt. %, and yet more preferably less than about 80 wt. % multistagelatex polymer, based on the total composition solids.

The multistage latex polymer is preferably prepared through chain-growthpolymerization, using one or more ethylenically unsaturated monomers.The polymerization reaction may be performed at a variety oftemperatures, e.g., a temperature in the range of about 10 to about 100°C. Examples of suitable ethylenically unsaturated monomers includeacrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, propylacrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate,ethyl methacrylate, propyl methacrylate, butyl methacrylate,2-ethylhexyl methacrylate, hydroxyethyl acrylate, hydroxyethylmethacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, glycidylmethacrylate, 4-hydroxybutyl acrylate glycidyl ether,2-(acetoacetoxy)ethyl methacrylate (AAEM), diacetone acrylamide,acrylamide, methacrylamide, methylol (meth)acrylamide, styrene, a-methylstyrene, vinyl toluene, vinyl acetate, vinyl propionate, allylmethacrylate, and mixtures thereof.

A preferred multistage latex polymer embodiment may also be made usingone or more hydrophobic monomers (e.g., tert-butyl (meth)acrylate, butylmethacrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,styrene, tert-butyl styrene and other monomers that will be familiar topersons having ordinary skill in the art of making latex polymers). Forexample, the multistage latex polymer could be made using at least 15wt. % butyl methacrylate based upon total latex polymer solids.

Preferred multistage latex polymers may also contain low levels ofstyrene. More preferably, they may contain very low levels of styrene.Most preferably, they may be substantially free of styrene.

Another preferred embodiment may be made using a functionalizedmultistage latex polymer, such as a polymer incorporating acetoacetylfunctionality. For example, acetoacetyl functionality may beincorporated into the polymer through the use of monomers such asacetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, allylacetoacetate, acetoacetoxybutyl methacrylate, 2,3-di(acetoacetoxy)propylmethacrylate, 2-(acetoacetoxy) ethyl methacrylate, t-butyl acetoacetate,diketene, and the like, or combinations thereof. In certain embodiments,the acetoacetyl functional latex polymer is preferably prepared throughchain-growth polymerization, using, for example, 2-(acetoacetoxy)ethylmethacrylate (AAEM). Preferred functionalized latex polymers include atleast about 0.5 wt. % functionality (e.g., acetoacetyl functionality),more preferably about 0.5 to about 5 wt. % functionality (e.g.,acetoacetyl functionality), and most preferably about 1 to about 4 wt. %functionality (e.g., acetoacetyl functionality), based on the totalweight of the latex polymer. Exemplary functionalized latex polymers aredescribed in U.S. Published Patent Application Nos. US 2006/0135684 A1and US 2006/0135686 A1, the disclosures of which are incorporated hereinby reference. Polymerizable hydroxy-functional or other active hydrogencontaining monomers may also be converted to the correspondingacetoacetyl functional monomer by reaction with diketene or othersuitable acetoacetylating agent (see, e.g., Comparison of Methods forthe Preparation of Acetoacetylated Coating Resins, Witzeman, J. S.; DellNottingham, W.; and Del Rector, F. J., Coatings Technology; Vol. 62,1990, 101 and the references contained therein). In preferred coatingcompositions, the acetoacetyl functional group is incorporated into thepolymer via 2-(acetoacetoxy) ethyl methacrylate, t-butyl acetoacetate,diketene, or combinations thereof.

The multistage latex polymer may also be prepared with a high Tgalkali-soluble polymer hard stage. Alkali-soluble polymers may beprepared by making a polymer with acrylic or methacrylic acid or otherpolymerizable acid monomer (usually at greater than 7 wt. %) andsolubilizing the polymer by addition of ammonia or other base. Examplesof suitable alkali-soluble high Tg support polymers include JONCRYL™ 675and JONCRYL 678 oligomer resins, available from BASF. A low Tg softstage monomer composition or gradient Tg composition could then bepolymerized in the presence of the hard stage alkali-soluble polymer toprepare a multistage latex polymer.

The ratios of monomers in the disclosed multistage latex polymers may beadjusted to provide the desired level of “hard” or “soft” segments. TheFox equation may be employed to calculate the theoretical Tg of apolymer made from two monomer feeds:

1/Tg=W _(a) /T _(ga) +W _(b) /T _(gb)

-   -   where T_(ga) and T_(gb) are the respective glass transition        temperatures of polymers made from monomers “a” and “b”; and        -   W_(a) and W_(b) are the respective weight fractions of            polymers “a” and “b”.            For example, a soft segment may be introduced by providing a            monomer composition containing 5 to 65 parts butyl acrylate,            20 to 90 parts butyl methacrylate, 0 to 55 parts methyl            methacrylate and 0.5 to 5 parts (meth)acrylic acid, and a            hard segment may be introduced by providing a monomer            composition comprising 0 to 20 parts butyl acrylate, 0 to 40            parts butyl methacrylate, 45 to 95 parts methyl methacrylate            and 0.5 to 5 parts (meth)acrylic acid. A soft segment may            also be introduced by providing a monomer composition            containing 5 to 65 parts butyl acrylate, 20 to 90 parts            butyl methacrylate, 0 to 55 parts methyl methacrylate, 0 to            5 parts (meth)acrylic acid and 0 to 20 parts            2-(acetoacetoxy)ethyl methacrylate (AAEM), and a hard            segment may be introduced by providing a monomer composition            containing 0 to 20 parts butyl acrylate, 0 to 40 parts butyl            methacrylate, 45 to 95 parts methyl methacrylate, 0 to 5            parts (meth)acrylic acid and 0 to 20 parts AAEM. The            aforementioned compositions are illustrative of this concept            and other compositions can be used in the practice of this            invention.

The latex polymers are typically stabilized by one or more nonionic oranionic emulsifiers, used either alone or together. Emulsifiers suitablefor use in the final topcoat composition will be known to persons havingordinary skill in the art or can be determined using standard methods.Examples of suitable nonionic emulsifiers includetert-octylphenoxyethylpoly(39)-ethoxyethanol,dodecyloxypoly(10)ethoxyethanol,nonylphenoxyethyl-poly(40)ethoxyethanol, polyethylene glycol 2000monooleate, ethoxylated castor oil, fluorinated alkyl esters andalkoxylates, polyoxyethylene (20) sorbitan monolaurate, sucrosemonococoate, di(2-butyl)phenoxypoly(20)ethoxyethanol,hydroxyethylcellulosepolybutyl acrylate graft copolymer, dimethylsilicone polyalkylene oxide graft copolymer, poly(ethyleneoxide)poly(butyl acrylate) block copolymer, block copolymers ofpropylene oxide and ethylene oxide,2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylated with 30 moles ofethylene oxide, N-polyoxyethylene(20)lauramide,N-lauryl-N-polyoxyethylene(3)amine and poly(10)ethylene glycol dodecylthioether. Examples of suitable anionic emulsifiers include sodiumlauryl sulfate, sodium dodecylbenzenesulfonate, potassium stearate,sodium dioctyl sulfosuccinate, sodium dodecyldiphenyloxide disulfonate,nonylphenoxyethylpoly(1)ethoxyethyl sulfate ammonium salt, sodiumstyrene sulfonate, sodium dodecyl allyl sulfosuccinate, linseed oilfatty acid, sodium, potassium, lithium or ammonium salts of phosphateesters of ethoxylated nonylphenol, sodium octoxynol-3-sulfonate, sodiumcocoyl sarcocinate, sodium 1-alkoxy-2-hydroxypropyl sulfonate, sodiumalpha-olefin (C₁₄-C₁₆) sulfonate, sulfates of hydroxyalkanols,tetrasodium N-(1,2-dicarboxy ethyl)-N-octadecylsulfosuccinamate,disodium N-octadecylsulfosuccinamate, disodium alkylamido polyethoxysulfosuccinate, disodium ethoxylated nonylphenol half ester ofsulfosuccinic acid and the sodium salt oftert-octylphenoxyethoxypoly(39)ethoxyethyl sulfate.

One or more water-soluble free radical initiators typically are used inthe chain growth polymerization of the multistage latex polymer.Initiators suitable for use in the final topcoat composition will beknown to persons having ordinary skill in the art or can be determinedusing standard methods. Representative water-soluble free radicalinitiators include hydrogen peroxide; tert-butyl peroxide; alkali metalpersulfates such as sodium, potassium and lithium persulfate; ammoniumpersulfate; and mixtures of such initiators with a reducing agent.Representative reducing agents include sulfites, such as alkali metalmetabisulfite, hydrosulfite, and hyposulfite; sodium formaldehydesulfoxylate; and reducing sugars such as ascorbic acid and isoascorbicacid. The amount of initiator is preferably from about 0.01 to about 3wt. %, based on the total amount of monomer. In a redox system theamount of reducing agent is preferably from 0.01 to 3 wt. %, based onthe total amount of monomer.

A variety of commercially-available multistage latex polymers may beused to prepare the disclosed final topcoat compositions. Representativesuch polymers are believed to include NEOCRYL™ XK-90, NEOCRYL™ XK-98,and NEOCRYL™ XK-230 multistage latex acrylic polymer emulsions(available from DSM NeoResins Inc. of Wilmington, Mass. and mixturesthereof.

The disclosed final topcoat compositions may contain one or moreoptional VOCs. VOCs suitable for use in the final topcoat compositionwill be known to persons having ordinary skill in the art or can bedetermined using standard methods. Desirably the final topcoatcompositions are low VOC, and preferably include less than 10 wt. %,more preferably less than 7 wt. %, and most preferably less than 4 wt. %VOCs based upon the total composition weight.

The disclosed final topcoat compositions may contain one or moreoptional coalescents to facilitate film formation. Coalescents suitablefor use in the final topcoat composition will be known to persons havingordinary skill in the art or can be determined using standard methods.Suitable coalescents include glycol ethers such as EASTMAN™ EP, EASTMANDM, EASTMAN DE, EASTMAN DP, EASTMAN DB and EASTMAN PM from EastmanChemical Co. and ester alcohols such as TEXANOL™ ester alcohol fromEastman Chemical Co. Preferably, the optional coalescent is a low VOCcoalescent such as is described in U.S. Pat. No. 6,762,230 B2, thedisclosure of which is incorporated herein by reference. The finaltopcoat compositions preferably include a low VOC coalescent in anamount of at least about 0.5 wt. %, more preferably at least about 1 wt.%, and yet more preferably at least about 1.5 wt. %. The final topcoatcompositions also preferably include a low VOC coalescent in an amountof less than about 10 wt. %, more preferably less than about 6 wt. %,and yet more preferably less than about 4 wt. %, based on the weight ofthe latex polymer.

The disclosed final topcoat compositions may contain one or moreoptional surface-active agents that modify the interaction of thetopcoat composition with the substrate or with a prior applied coating.The surface-active agent affects qualities of the composition includinghow the composition is handled, how it spreads across the surface of thesubstrate, and how it bonds to the substrate. In particular, the agentcan modify the ability of the composition to wet a substrate.Surface-active agents may also provide leveling, defoaming or flowcontrol properties, and the like. Surface-active agents suitable for usein the final topcoat composition will be known to persons havingordinary skill in the art or can be determined using standard methods.If used, the surface-active agent is preferably present in an amount ofless than 5 wt. %, based on the total weight of the topcoat composition.Surface-active agents suitable for use in the final topcoat compositionwill be known to persons having ordinary skill in the art or can bedetermined using standard methods. Exemplary surface-active dispersingor wetting agents include those available under the trade designationsSTRODEX™ KK-95H, STRODEX PLF100, STRODEX PKOVOC, STRODEX LFK70, STRODEXSEK50D and DEXTROL™ 0050 from Dexter Chemical L.L.C. of Bronx, N.Y.;HYDROPALAT™ 100, HYDROPALAT 140, HYDROPALAT 44, HYDROPALAT 5040 andHYDROPALAT 3204 from Cognis Corp. of Cincinnati, Ohio; LIPOLIN™ A,DISPERS™ 660C, DISPERS 715W and DISPERS 750W from Degussa Corp. ofParsippany, N.J.; BYK™ 156, BYK 2001 and ANTI-TERRA™ 207 from Byk Chemieof Wallingford, Conn.; DISPEX™ A40, DISPEX N40, DISPEX R50, DISPEX G40,DISPEX GA40, EFKA™ 1500, EFKA 1501, EFKA 1502, EFKA 1503, EFKA 3034,EFKA 3522, EFKA 3580, EFKA 3772, EFKA 4500, EFKA 4510, EFKA 4520, EFKA4530, EFKA 4540, EFKA 4550, EFKA 4560, EFKA 4570, EFKA 6220, EFKA 6225,EFKA 6230 and EFKA 6525 from Ciba Specialty Chemicals of Tarrytown,N.Y.; SURFYNOL™ CT-111, SURFYNOL CT-121, SURFYNOL CT-131, SURFYNOLCT-211, SURFYNOL CT 231, SURFYNOL CT-136, SURFYNOL CT-151, SURFYNOLCT-171, SURFYNOL CT-234, CARBOWET™ DC-01, SYRFYNOL 104, SURFYNOLPSA-336, SURFYNOL 420, SURFYNOL 440, ENVIROGEM™ AD-01 and ENVIROGEM AE01from Air Products & Chemicals, Inc. of Allentown, Pa.; TAMOL™ 1124,TAMOL 850, TAMOL 681, TAMOL 731 and TAMOL SG-1 from Rohm and Haas Co. ofPhiladelphia, Pa.; IGEPAL™ CO-210, IGEPAL CO-430, IGEPAL CO-630, IGEPALCO-730, and IGEPAL CO-890 from Rhodia Inc. of Cranbury, N.J.; T-DET™ andT-MULZ™ products from Harcros Chemicals Inc. of Kansas City, Kans.;polydimethylsiloxane surface-active agents (such as those availableunder the trade designations SILWET™ L-760 and SILWET L-7622 from OSISpecialties, South Charleston, W. Va., or BYK 306 from Byk-Chemie) andfluorinated surface-active agents (such as that commercially availableas FLUORAD FC-430 from 3M Co., St. Paul, Minn.). The surface-activeagent may include a defoamer. Exemplary defoamers include BYK 018, BYK019, BYK 020, BYK 022, BYK 025, BYK 032, BYK 033, BYK 034, BYK 038, BYK040, BYK 060, BYK 070 and BYK 077 from Byk Chemie; SURFYNOL DF-695,SURFYNOL DF-75, SURFYNOL DF-62, SURFYNOL DF-40 and SURFYNOL DF-110D fromAir Products & Chemicals, Inc.; DEEFO™ 3010A, DEEFO 2020E/50, DEEFO 215,DEEFO 806-102 and AGITAN™ 31BP from Munzing Chemie GmbH of Heilbronn,Germany; EFKA 2526, EFKA 2527 and EFKA 2550 from Ciba SpecialtyChemicals; FOAMAX™ 8050, FOAMAX 1488, FOAMAX 7447, FOAMAX 800, FOAMAX1495 and FOAMAX 810 from Degussa Corp.; FOAMASTER™ 714, FOAMASTER A410,FOAMASTER 111, FOAMASTER 333, FOAMASTER 306, FOAMASTER SA-3, FOAMASTERAP, DEHYDRAN™ 1620, DEHYDRAN 1923 and DEHYDRAN 671 from Cognis Corp.

The disclosed final topcoat compositions may contain one or moreoptional pigments. Pigments suitable for use in the final topcoatcomposition will be known to persons having ordinary skill in the art orcan be determined using standard methods. Exemplary pigments includetitanium dioxide white, carbon black, lampblack, black iron oxide, rediron oxide, yellow iron oxide, brown iron oxide (a blend of red andyellow oxide with black), phthalocyanine green, phthalocyanine blue,organic reds (such as naphthol red, quinacridone red and toluidine red),quinacridone magenta, quinacridone violet, DNA orange, or organicyellows (such as Hansa yellow). The final topcoat composition may alsoinclude a gloss control agent or an optical brightener agent, such asUVITEX™ OB optical brightener, available from Ciba Specialty Chemicalsof Tarrytown, N.Y.

In certain embodiments it is advantageous to include fillers or inertingredients in the topcoat composition. Fillers or inert ingredientsextend, lower the cost of, alter the appearance of, or provide desirablecharacteristics to the composition before and after curing. Fillers andinert ingredients suitable for use in the final topcoat composition willbe known to persons having ordinary skill in the art or can bedetermined using standard methods. Exemplary fillers or inertingredients include clay, glass beads, calcium carbonate, talc, silicas,feldspar, mica, barytes, ceramic microspheres, calcium metasilicates,organic fillers and the like. Fillers or inert ingredients arepreferably present in an amount of less than about 15 wt. %, based onthe total weight of the topcoat composition.

In certain applications it may also be desirable to include biocides orfungicides. Exemplary biocides or fungicides include ROZONE™ 2000,BUSAN™ 1292 and BUSAN 1440 from Buckman Laboratories of Memphis, Term.;POLYPHASE™ 663 and POLYPHASE 678 from Troy Chemical Corp. of FlorhamPark, N.J. and KATHON™ LX from Rohm and Haas Co.

The final topcoat may also include other optional ingredients thatmodify properties of the topcoat composition as it is stored, handled,or applied, or at other or subsequent stages. Waxes, flatting agents,rheology control agents, mar and abrasion additives, and other similarperformance-enhancing additives may be employed as needed in amountseffective to upgrade the performance of the final topcoat compositionand the dried or otherwise hardened topcoat. Exemplary wax emulsions toimprove coating physical performance include MICHEM™ Emulsions 32535,21030, 61335, 80939M and 7173MOD from Michelman, Inc. of Cincinnati,Ohio and CHEMCOR™ 20N35, 43A40, 950C25 and 10N30 from ChemCor ofChester, N.Y. Exemplary rheology control agents include RHEOVIS™ 112,RHEOVIS 132, RHEOVIS152, VISCALEX™ HV30, VISCALEX AT88, EFKA 6220 andEFKA 6225 from Ciba Specialty Chemicals; BYK 420 and BYK 425 from BykChemie; RHEOLATE™ 205, RHEOLATE 420 and RHEOLATE 1 from ElementisSpecialties of Hightstown, N.J.; ACRYSOL™ L TT-615, ACRYSOL RM-5,ACRYSOL RM-6, ACRYSOL RM-8W, ACRYSOL RM-2020 and ACRYSOL RM-825 fromRohm and Haas Co.; NATROSOL™ 250LR from Hercules Inc. of Wilmington,Del. and CELLOSIZE™ QP09L from Dow Chemical Co. of Midland, Mich.Desirable performance characteristics of the coating include chemicalresistance, abrasion resistance, hardness, gloss, reflectivity,appearance, or combinations of these characteristics, and other similarcharacteristics. For example, the topcoat may contain abrasionresistance promoting adjuvants such as silica or aluminum oxide (e.g.,sol-gel processed aluminum oxide).

A variety of other optional additives may be used in the disclosed finaltopcoat compositions and will be familiar to persons having ordinaryskill in the art, including those described in Koleske et al., Paint andCoatings Industry, April 2003, pages 12-86. For example, the finaltopcoat compositions may include one or more performance or propertyenhancing additives such as colorants, dyes, thickeners, heatstabilizers, leveling agents, anti-cratering agents, curing indicators,plasticizers, sedimentation inhibitors, ultraviolet-light absorbers, andthe like. Also, for application using factory coating equipment (e.g.,curtain coaters), the composition may employ additives tailored to thechosen equipment and installation. Such additives typically are selectedon a site-by-site basis using standard methods that will be familiar topersons having ordinary skill in the art.

The final topcoat composition may be applied to the optionally sealed orprimed substrate using any suitable application method. For example, thetopcoat composition may be roll coated, sprayed, curtain coated, vacuumcoated, brushed, or flood coated using an air knife system. Preferredapplication methods provide a uniform coating thickness and are costefficient. Especially preferred application methods employ factoryequipment that moves the board past a coating head and thence pastsuitable drying or curing equipment. The coating covers at least aportion of the first major surface of the board, and desirably coversthe entire first major surface, in a substantially uniformly thicklayer.

The disclosed final topcoat compositions preferably have a PVC less than45%, more preferably less than about 40%, and most preferably about 10to about 35%. The final topcoat compositions also preferably have anMFFT of about 0 to about 55° C., and more preferably about 0 to about20° C., when tested with a RHOPOINT™ 1212/42 MFFT-60 bar instrument,available from Rhopoint Instruments Ltd. of East Sussex, United Kingdom.

It has been found that the thickness of the topcoat layer can affect theperformance of the present invention. For example, if the topcoat is toothin the finished board may not achieve the desired performance,weatherability and appearance. If the topcoat is too thick the costs ofthe system will unnecessarily increase. A recommended thickness for thedried or otherwise hardened final topcoat is between about 20 and about200 micrometers, preferably between about 25 and about 120 micrometers,more preferably between about 30 and about 100 micrometers, and mostpreferably between about 35 and about 75 micrometers.

The topcoat may be hardened into a paint film using any suitable process(e.g., two-part curing mechanism, radiation curing, air drying, heatcuring, etc.). More preferably, the topcoat is hardened without the needto heat the cement substrate to a high temperature. Although the use ofsuch a heating process is within the scope of the present invention, itis somewhat less efficient for cement-based products given their lowheat transfer characteristics. Consequently, preferred processesgenerally employ board surface temperatures of less than 100° C., morepreferably less than 90° C., and most preferably less than 80° C.Radiation hardened systems (e.g., UV or visible-light cured systems) ormulti-component systems (e.g., two-part systems) may be utilized.Multi-component systems may be hardened, for example, by mixing thecomponents prior to or during application to the substrate and allowingthe mixed components to harden on the substrate. Other low temperaturehardened systems will be known to persons having ordinary skill in theart or can be determined using standard methods, and may be utilized ifdesired.

The disclosed prefinished boards may be stacked using one or more linersbetween adjacent boards. Exemplary liners include sheet and filmmaterials that can help protect the boards from damage. The liners may,if desired, adhere lightly to the board face (thereby helping keep theliner against the board surface) or simply remain in place by friction.In a preferred embodiment, board pairs are stacked in face-to-facerelationship with a liner disposed between the faces to form acrush-resistant unit. A plurality of these units may then be stacked toform a larger stack. Exemplary liners include paper, plastic, foam,non-woven or fabric sheets and film materials. Preferred liners includeplastic sheets to protect the finished board from rubbing and scrapingdamage during transport and installation. The liner may have a varietyof thickness, e.g., between about 20 and about 100 micrometers.

The disclosed final topcoats resist crush damage. Crush resistance maybe visually assessed and rated using a 1 to 5 rating scale, as describedbelow, with 5 being essentially no damage and 1 being severe damage ofthe coating. The final topcoat provides crush resistance of at least 3,more preferably at least 4 and most preferably 5 when two face-to-facecoated embossed substrates are subjected to a pressure of about 6kg/cm², more preferably about 8 kg/cm², and most preferably about 10kg/cm². For example, the test board samples preferably achieve a ratingof 3 or greater, more preferably 4 or greater, and optimally 5, whentested at a pressure of about 8 kg/cm². The Crush Resistance visualassessment may be carried out as follows:

Substrate Preparation

A 15 cm×21 cm factory primed wood grain embossed fiber cement sidingboard (HARDIEPLANK lap siding, SELECT CEDARMILL grade, available fromJames Hardie Building Products, Inc.) is preheated to 46-54° C. in ahigh velocity hot air oven with a 149° C. airstream for 60 seconds, thencoated with the final topcoat composition using a paint brush and enoughmaterial to provide a dry film thickness (DFT) of about 28 micrometers.Immediately after applying the first coat, the coated board is placed inthe oven for 20 seconds to bring the board surface temperature (BST) to43-52° C. After a 10 second flash-off time, the board is recoated withthe final topcoat using the paint brush and enough material to provideabout 28 micrometer DFT and total about 56 micrometer DFT. The coatedboard is then returned to the oven and force dried for 60 seconds to a70 to 90° C. BST. The coated board is removed from the oven and cooledto about 49° C. BST, covered with a 0.0038 to 0.0064 mm thick sheet ofINTEGRAL™ 816 polyolefin protective liner (available from Dow ChemicalCompany of Midland, Mich.). A second, similarly coated and liner-coveredboard with about a 49° C. BST is placed face-to-face with the testboard. Both boards (with the two protective sheets between them) areplaced in a hydraulic press whose platens have been heated to about 49°C. and subjected to a test pressure (e.g., 6, 8 or 10 kg/cm²,corresponding to 85, 114 or 142 p.s.i.) for 5 minutes. The boards areremoved from the press, and those portions of the test board embossedwith a tight wood grain pattern are evaluated according to the ratingscale shown below in Table 1. An average rating for three test samplesis recorded.

TABLE 1 Visual Assessment Rating value Appearance of the panel 1Obviously crushed: Peaks are severely crushed and the grain pattern fromthe opposing board is embossed into the coating, causing severewrinkling of the coating around the damaged area. 2 Moderately crushed:Peaks show flattening to widths over 4 mm, and the grain pattern fromthe opposing board is slightly embossed into the coating 3 Slightlycrushed: Many peaks show flattening to a width of 2 mm to 4 mm. 4 Veryslightly crushed: A few peaks show peak flattening to a width less than2 mm. 5 Uncrushed: no crushed peaks or glossy spots are visible to theunaided eye or with 5X magnification.

As shown in the following Examples, fiber cement products having a finaltopcoat system of the present invention provide significant crushresistance compared to fiber cement products that do not incorporate theimproved topcoat system.

Example 1 Multistage Latex Polymer A

NEOCRYL™ XK-90 multistage latex acrylic polymer emulsion (available fromDSM NeoResins Inc. of Wilmington, Mass. was subjected to DSC analysisusing a Q SERIES™ DSC thermal analysis instrument from TA Instruments ofNew Castle, Del. FIG. 5 shows the DSC curve, and demonstrates that thepolymer exhibited two distinct Tg values, namely a soft stage Tg atabout 3.4° C. and a hard stage Tg at about 96.6° C.

Example 2 Multistage Latex Polymer B

An acetoacetyl functional multistage latex polymer was prepared from afirst monomer mixture containing butyl acrylate, butyl methacrylate, andmethacrylic acid and a second monomer mixture containing methylmethacrylate, butyl methacrylate and methacrylic acid. FIG. 6 shows theDSC curve, and demonstrates that the polymer exhibited two distinct Tgvalues, namely a soft stage Tg at about 7.6° C. and a hard stage Tg atabout 98.5° C.

Example 3 Multistage Latex Polymer C

A multistage latex polymer was prepared from a first monomer mixturecontaining butyl acrylate, butyl methacrylate, acrylic acid andmethacrylic acid and a second monomer mixture containing butyl acrylate,methyl methacrylate and methacrylic acid. FIG. 7 shows the DSC curve,and demonstrates that the polymer exhibited two distinct Tg values,namely a soft stage Tg at about 0.7° C. and a hard stage Tg at about91.7° C.

Example 4 Multistage Latex Polymer D

An acetoacetyl functional multistage latex polymer was prepared from afirst monomer mixture containing 2-ethylhexyl acrylate, butylmethacrylate, AAEM and methacrylic acid and a second monomer mixturecontaining methyl methacrylate, butyl methacrylate, AAEM and methacrylicacid. FIG. 8 shows the DSC curve, and demonstrates that the polymerexhibited two distinct Tg values, namely a soft stage Tg at about 10° C.and a hard stage Tg at about 89.2° C.

Comparison Example 5 Single Stage Latex Polymer E

ACRONOL OPTIVE™ 220 aqueous acrylic ester copolymer dispersion(available from BASF Corporation of Florham Park, N.J.) was subjected toDSC analysis. FIG. 9 shows the DSC curve, and demonstrates that thepolymer exhibited a single Tg at about 17.3° C.

Comparison Example 6 Single Stage Latex Polymer F

RHOPLEX™ AC-2829 acrylic polymer emulsion (available from Rohm and HaasCompany of Philadelphia, Pa.) was subjected to DSC analysis. FIG. 10shows the DSC curve, and demonstrates that the polymer exhibited asingle Tg at about 16.4° C.

Comparison Example 7 Single Stage Latex Polymer G

A single stage latex polymer was prepared using butyl acrylate, methylmethacrylate, methacrylic acid and acrylic acid. FIG. 11 shows the DSCcurve, and demonstrates that the polymer exhibited a single Tg at about16.6° C.

Examples 8-11 Multistage Latex Polymer Topcoat Compositions

In a mixing vessel equipped with a high-speed mixer and dispersionblade, the ingredients shown below in Table 2 were added in the listedorder. Final topcoat compositions were formed by adding the first twoingredients, mixing for 5 minutes until homogeneous, adding the next 5ingredients, mixing at high speed for 15 minutes, then adding theremaining 6 ingredients and mixing for 15 minutes using moderateagitation. Fiber cement siding boards with a moisture content of about12% were topcoated with the resulting compositions and evaluated usingthe Visual Assessment of Crush Resistance scale described above andabout 8 kg/cm² test pressure for 5 minutes. The results are shown in thelast line of Table 2:

TABLE 2 Ingredient Example 8 Example 9 Example 10 Example 11 Water 100100 100 100 Thickener⁽¹⁾ 0.7 0.7 0.7 0.7 Defoamer⁽²⁾ 1.5 1.5 1.5 1.5Coalescent⁽³⁾ 15 15 15 15 Dispersant⁽⁴⁾ 7 7 7 7 Pigment⁽⁵⁾ 217 217 217217 Extender⁽⁶⁾ 84 84 84 84 Neutralizer⁽⁷⁾ 2 2 2 2 Water 8 8 8 8 Example1 latex 626 — — — Example 2 latex — 580 — — Example 3 latex — — 580 —Example 4 latex — — — 580 Water 20 60 60 60 Defoamer⁽⁸⁾ 1 1 1 1Thickener⁽⁹⁾ 1.5 1.5 1.5 1.5 Crush Resistance 3 4 3 3 ⁽¹⁾CELLOSIZE ™ QP09L hydroxyethyl cellulose, available from Dow Chemical Company ofMidland, MI. ⁽²⁾DEHYDRAN ™ 1620, available from Cognis Corporation ofCincinnati, OH. ⁽³⁾TEXANOL ™ ester alcohol, available from EastmanChemical Company of Kingsport, TN. ⁽⁴⁾DISPERBYK ™ 190 block copolymersolution, available from Byk-Chemie USA of Wallingford, CT. ⁽⁵⁾TI-PURE ™R902-28 titanium dioxide, available from E. I. DuPont de Nemours andCompany of Wilmington, DE. ⁽⁶⁾ASP 170 aluminum silicate, available fromEnglehard Corporation of Iselin, NJ. ⁽⁷⁾Ammonium hydroxide, 26%,available from Aldrich Chemical ⁽⁸⁾BYK ™ 024 polysiloxane defoamer,available from Byk-Chemie USA of Wallingford, CT. ⁽⁹⁾ACRYSOL ™RM-2020NPR hydrophobically modified ethylene oxide urethane blockcopolymer, available from Rohm and Haas Company of Philadelphia, PA.

As shown in Table 2, each of the final topcoat compositions provided acrush-resistant coating. These coatings should readily withstand storageat the bottom of at least a two pallet stack of coated boards.

Comparison Examples 12-14 Single Stage Latex Polymer TopcoatCompositions

In a mixing vessel equipped with a high-speed mixer and dispersionblade, the ingredients shown below in Table 3 were added in the listedorder. Final topcoat compositions were formed by adding the first twoingredients, mixing for 5 minutes until homogeneous, adding the next 5ingredients, mixing at high speed for 15 minutes, then adding theremaining 6 ingredients and mixing for 15 minutes using moderateagitation. Fiber cement siding boards with a moisture content of about12% were topcoated with the resulting compositions and evaluated usingthe Visual Assessment of Crush Resistance scale described above andabout 8 kg/cm² test pressure for 5 minutes. The results are shown in thelast line of Table 3:

TABLE 3 Comparison Comparison Comparison Ingredient Example 12 Example13 Example 14 Water 100 100 100 Thickener⁽¹⁾ 0.7 0.7 0.7 Defoamer⁽²⁾ 1.51.5 1.5 Coalescent⁽³⁾ 15 15 15 Dispersant⁽⁴⁾ 7 7 7 Pigment⁽⁵⁾ 217 217217 Extender⁽⁶⁾ 84 84 84 Neutralizer⁽⁷⁾ 1 1 1 Water 8 8 8 Comparison 570— — Example 5 latex Comparison — 526 — Example 6 latex Comparison — —533 Example 7 latex Water 76 116 110 Defoamer⁽⁸⁾ 1 1 1 Thickener⁽⁹⁾ 1.51.5 1.5 Crush Resistance 2 1 2 ⁽¹⁾CELLOSIZE ™ QP 09L hydroxyethylcellulose, available from Dow Chemical Company of Midland, MI.⁽²⁾DEHYDRAN ™ 1620, available from Cognis Corporation of Cincinnati, OH.⁽³⁾TEXANOL ™ ester alcohol, available from Eastman Chemical Company ofKingsport, TN. ⁽⁴⁾DISPERBYK ™ 190 block copolymer solution, availablefrom Byk-Chemie USA of Wallingford, CT. ⁽⁵⁾TI-PURE ™ R902-28 titaniumdioxide, available from E. I. DuPont de Nemours and Company ofWilmington, DE. ⁽⁶⁾ASP 170 aluminum silicate, available from EnglehardCorporation of Iselin, NJ. ⁽⁷⁾Ammonium hydroxide, 26%, available fromAldrich Chemical ⁽⁸⁾BYK ™ 024 polysiloxane defoamer, available fromByk-Chemie USA of Wallingford, CT. ⁽⁹⁾ACRYSOL ™ RM-2020NPRhydrophobically modified ethylene oxide urethane block copolymer,available from Rohm and Haas Company of Philadelphia, PA.

As shown in Table 3, none of the comparison topcoat compositionsprovided a crush-resistant coating.

Having thus described the preferred embodiments of the presentinvention, those of skill in the art will readily appreciate that theteachings found herein may be applied to yet other embodiments withinthe scope of the claims hereto attached. The complete disclosure of allpatents, patent documents, and publications are incorporated herein byreference as if individually incorporated.

We claim:
 1. A coated fiber cement article comprising an unattachedfiber cement board roofing tile or roofing slate substrate having afirst major surface at least a portion of which is covered with a crushresistant final topcoat composition comprising a multistage latexpolymer.
 2. The article of claim 1, wherein the multistage latex polymerhas a gradient Tg.
 3. The article of claim 1, wherein the multistagelatex polymer comprises at least one soft stage having a Tg less thanabout 40° C. and at least one hard stage having a Tg greater than about40° C.
 4. The article of claim 1, wherein the multistage latex polymercomprises at least one soft stage having a Tg between about −15 andabout 15° C. and at least one hard stage having a Tg between about 60and about 105° C.
 5. The article of claim 1, wherein the multistagelatex polymer comprises about 50 to about 90 wt. % soft stage polymermorphology and about 10 to about 50 wt. % hard stage polymer morphologybased on the total multistage latex polymer weight.
 6. The article ofclaim 1, wherein the multistage latex polymer has a soft stage Tg suchthat the topcoat composition will coalesce at a Minimum Film FormingTemperature (MFFT) between about 0 and about 55° C. without requiringmore than 10% VOCs for acceptable film formation.
 7. The article ofclaim 1, wherein the topcoat composition has a minimum film formingtemperature less than about 20° C.
 8. The article of claim 1, whereinthe topcoat composition comprises at least about 10 wt. % multistagelatex polymer.
 9. The article of claim 1, wherein the multistage latexpolymer is functionalized.
 10. The article of claim 1, wherein themultistage latex polymer comprises acetoacetyl functionality.
 11. Thearticle of claim 1, wherein the multistage latex polymer was formed fromone or more ethylenically unsaturated monomers and less than about 20wt. % styrene was used to form the multistage latex polymer based uponthe total weight of such ethylenically unsaturated monomers used to formsuch polymer.
 12. The article of claim 1, wherein the topcoatcomposition includes less than 7 wt. % volatile organic compounds. 13.The article of claim 1, wherein the topcoat composition includes lessthan 4 wt. % volatile organic compounds.
 14. The article of claim 1,wherein the topcoat composition further comprises at least about 1 wt. %low VOC coalescent and has a pigment volume concentration less than 45%.15. The article of claim 1, wherein the topcoat has a Crush Resistancevalue of at least 3 when two face-to-face coated profiled or embossedfiber cement board substrates are subjected to a pressure of about 6kg/cm².
 16. The article of claim 1, wherein the topcoat will change lessthan 10 Macadam units following a 5 year vertical exterior exposure inFlorida.
 17. The article of claim 1, wherein the topcoat has a chalkrating not less than 5 when evaluated according to ASTM D 4214 TestMethod A using a 5 year vertical exterior exposure in Florida.
 18. Thearticle of claim 1, wherein the substrate comprises an unattached fibercement board roofing tile.
 19. The article of claim 1, wherein thesubstrate comprises an unattached fiber cement board roofing slate. 20.The article of claim 1, further comprising a pallet loaded with one ormore stacks containing a plurality such roofing tiles or slates.